Insulated cable having strand shielding semi-conductive layer

ABSTRACT

This invention relates to an insulated cable having an extruded strand shielding semi-conductive layer, and especially to an insulated cable which is characterized by using a blend of high density polyethylene and ethylene propylene rubber as the extruded strand shielding semi-conductive layer, the quantitative ratio of the high density polyethylene in the blend being 20 - 50 weight percent.

United States Patent 1 Shiga et a1. 3

[ INSULATED CABLE HAVING STRAND SHIELDING SEMI-CONDUCTIVE LAYER [75] inventors: Tetsuya Shiga; Yutaka lnagaki;

Hironaga Matsubara, all of Osaka, Japan [7 3] Assignee: Sumitomo Electric lndustires, Ltd.,

l-ligashi-ku, Osaka, Japan 22 Filed: M 1166.22, 1971 21" Appl. N6.;2'1 1,072'

[30] Foreign Application Priority Date Dec. 28, 1970 Japan 45/24503 [52] US. Cl.l74/102 SC, 174/110 AR, 174/110 PM, 174/120 SC [51] Int. Cl. H011) 3/30, HOlb 7/02 [58] Field of Search..; 174/102 SC, 105 SC,

174/106 SC, 120 SC, 120 R, 120 AR, 120 SR, 110PM, 110 AR,110 SR, 126 R, 127, 36; 1l7/2l5,216, 230, 231,232

[56] References Cited UNITED STATES PATENTS 3,262,988 7/1966 Joyce 1171232 x 3,375,303

3/1968 Joyce 117/232 X lNSULATM/G L/wse [451 July3l, 1973 p E IG PATENTS OR APPLICA I NS 633,259 AZ/19162 may n t 110191711;

Primary Examiner-Bernard A. Gilheany Assistant Examiner-A. T. Grimley Attorney-Carothers and Carothers 57 ABSTRACT This invention relates to an insulated cable-havingan extruded strand shielding semi-conductive layer, and especially to an insulated cable which is characterized by using a blend of high density polyethylene and ethylene propylene rubber as the eitruded strand shielding semi-conductive layer, the quantitative ratio of the high density polyethylene in the blend being 20 50 weight percent.

3 (ilailns, 1 Drawing Figure. I I

Su /W050 C uaucroe PAIENIED JUL 3 I I975 $EM/ Cououcnve lNsuLAr/u LAYE'E STRANDED Cb uoucroe INSULATED CABLE HAVING STRAND SHIELDING SEMI-CONDUCTIVE LAYER BACKGROUND OF THE INVENTION This invention relates to an extruded strand shielding semi-conductive layer for plastic insulated cable.

In the customary plastics insulated cable which requires a needs strand shielding semi-conductive layer, 1 a sufficient quantity of carbon-black is mingled in the layer to impart conductivity to the copolymer, which mainly consists of ethylene. Also, across-linking agent, anti-oxydant and processing-aid agent are blended into I and extruded within the semiconductive layer to improve the strand shielding. Recently, in order to produce these kind of cable efficiently and with superior properties, double or triple extrusion i.e. extrusion of the strand shielding semi-conductive layer, extrusion of the insulating layer and extrusion of the insulation shielding semi-conductive layer etc., are usually performed by a continuous tandem process to produce the cable. In such a process, wherein extruded strand shielding semi-conductive materials with the above mentioned blend are used, defects occur in that the inner semi-conductive layer to be extruded tends to clog the point of the extruder for the insulating layer due to its soft property, and more significantly, the boundary face between the extruded insulating layer and the extruded strand shielding semi-conductive layer becomes rough and extremely sharp edges are produced such that the breakdown voltage of the cable remarkably decreases.

In regard to these defects, the present inventors repeated various investigations, and as a result thereof, completed a composite for an extruded strand shielding semi-conductive layer which completely resolves all of the above-mentioned defects.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a cross sectional view of a cable show- DETAILED DESCRIPTION OF THE INVENTION gravity above 0.930 at C) with 80 50 weight parts l of ethylene propylene rubber (EPM, EPDM etc.).per

I00 weight parts of blend, and further mixing carbon black therein as a conductive material. This mixture is then extruded to coat the inner conductor. When it is necessary, of course, other cross-linking agents, antioxydants or processing-aid-agents may be blended in accordance with the conditions of cable use. As a result of the experiments performed by the present inventors, it was confirmed that quantity of the additions of carbon black (25 weight parts for weight parts of base polymer), anti-oxydants, such as the amine group or the phenol group, and processing aid agents, such as Zinc stearate, and cross-linking agents have no influence on ultimate electric properties of the semiconductive layer.

Practical examples and reference examples are shown in the following Table l.

The materials and methods of testing used in this practice are as follows: MM

The strand shielding semi-cond'uctive'layer indicated in Table l was extruded on a conductorwith strands having a 100 mm cross-sectional area. In addition, the insulating layer identified in Table I was extruded on the layer by the continuous tandem process in order to coat it, then cross-linking reaction of the layer was completed by using saturated water vapor at a pressure of 15 atmospheres. (However in practicalexample l l, the crosslinking reaction was not performed.) Then, the electric properties (breakdown voltage) of cable were examined. The quality of the results are shown in Table l by the following symbols:

ing the relationship of the semi-conductive blend of 45 A: excellent high density polyethylene and ethylene rubber to the B: good stranded conductor and the outer insulating layer. C: inferior TABLE 1 Cross-linking agent Strand shielding for semi- Electric I semiconductive layer conductive charac- No. Insulating layer basepolymer layer teristics Ref. ex. 1 Polyethylene specific EA None C gravity 0.92 MI =2 DCI'"= 2.5% Anti-oxydant 0.3% Ref. ex. 2 Do. 'EA DCP= 2% C Ref. ex.3 Do. EVA C I amountoi'Vinylacetatc=5% Ref. ex. 4 D0. EVA Do. C

.fi mqfvinvl acetate= 0% Ref.ex.5 Do. EVA Do. C

L amount of Vinyl Reiexhfi Do. EVA m. r

I 211mm 01 my] aeaaze= 30% Ref. ex. 7 Do. EVA DCP==2% amount of Vinyl acetate=40% Ref. ex. 8 Do. EVA None C amount ofVinyl acetate= 20% TAB LE 1- Continued Cross-linking agent Strand shielding for semi- Electric semiconductive layer conductive charac- No. Insulating layer base polymer layer teristics Ref. ex. 9 Do. llzlloll yethylene sp.gr. 0.92 None C '7 Reflex. Do. Do. DCP=2% C Ref. ex. 1 I Do. high density None B Polyethylene sp.gr. 0.96 Ref. ex. l2 Do. Do. DCP= 1% B Ref. ex. l3 Do. Polypropylene None B Ref. ex. 14 Do. Ethylene propylene DCP=2% B rubber (EP rubber) Ref. ex. Do. Butyl rubber Act r C Q= 0.5% DM 1% Ref. ex. 16 Do. High density None polyethylene (weight) sp.gr.=0.96 EP rubber 90% Prac. ex. I Do. High density Do. A

polyethylene EP rubber 80% Prac. ex. 2 Do. High density Do. A

polyethylene EP rubber 70% Prac. ex. fl Do. High density Do. A

polyethylene EP rubber 60% Prac. ex. 4 Do. High density None A polyethylene EP rubber 50% Prac. ex. 5 Do. High density X= l.5 A

polyethylene 40% EP rubber 60% Ref. ex. 17 Do. High density None B polyethylene 60% EP rubber 40% Ref. ex. 18 Do. High density Do. B

polyethylene 80% EP rubber 20% Ref. ex. l9 Do. High density Do. B

polyethylene 50% Butyl ntbber 50% Ref. ex. 20 Do. Low density Do. B

polyethylene 40% EP rubber 60% Ref. ex. 21 Do. Polypropylene 40% Do. B

EP rubber 60% Prac. ex. 6 Polyethylene sp.gr.=0.92 High density Do. A

Ml 4 polyethylene 40% DCP=2.5% EP rubber 60% anti-oxyda'nt agent=0.3% Prac. ex. 7 talc of 30 weight parts is Do. Do. A.

added to composite in practical example 6 of I00 weight part Prac. ex. 8 clay of 30 weight parts is Do. Do. A

added to Composite in practical example 6 of I00 weight parts Prac. ex. 9 EVA Do. Do. A

(amount ofvinyl acetate= l5%) M l= 3 DCP= 2.5% anti-oxydant= 0.3% Prac. tale of 30 weight pans is Do. Do. A

ex. l0 added to composite in practical example 9 of I00 weight pan Prac. polyethylene sp.gr. 0.92 Do. Do. A

ex. l l Ml=0.2

Not

f EVA: ethylene-vinylacetate copolymer Actor Q: p-Benzoquinone-dioxime Actor DM: 2-Benzothiazolyl-disultidewhich are (trademarks of Kawaguchi Chemical Co.)

" X: 2.5-dimcthyl-2,5'-di(tertiary class butyl peroxi)-hexene-3 As shown in the practical examples of Table l, the objective cable which has superior breakdown voltage characteristic, can be obtained only when high density polyethylene and ethylene propylene rubber are blended at a certain ratio. When the weight percent of the high density polyethylene is below 20 or above 50, the breakdown voltage decreases in both cases. Accordingly, high a breakdown voltage can be obtained only when the weight percent of the high density polyethylene is in the range of 20 50. Furthermore, it was also found that when this combination is changed by using other polymers, good result can not be obtained.

property to the layer is not specifically defined, but

when it is below 25 percent, the necessary conductivity for this application can not be obtained, and when it is above percent, the processing properties of the blend become remarkably inferior. Accordingly it is preferable that it be in the range of 25 75 percent.

ing semi-conductive layer comprising a blend of high density polyethylene and ethylene propylene rubber with the ratio of weight percent of high density polyethylene in the blend being in the range of-20 50 and an 5 addition of conductive material.

2. The insulated cable of claim 1 wherein said conductive material is carbon black. 3; The insulated cable of claim 2 wherein the amount of said carbon black included in said blend is in the 10 range of 27 75 percent.

i 1 OFFICE 7' 1 R C N g i 7 9 I D ted- July "31, 1973 1 l nr n toflsf T -5 2 i-i 9 'a I ag i; flironaga'Mat'sqbgrd It; is" certified that Qrror appears in the .above idfififigd*patent and that said Lette rsiratept are ,hereby correctedjas shown-below:

Signed ah ed hiszand day jdi Janu r 1974'.

tfcst;

"En'w D .FLETcHER,JR;-f I RENE D; TEGTME YER 3 T A te ng fficer Acting Commissioner f Patents;

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 1 1 Dated July 3]., 19 73 Inventofls) suy Shiga; Yutaka Inagaki; Hironaga Matsubara It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected -as shown below:

Signed and sealed this 22nd day of January 1974.

(SEAL) Attest:

EDWARD M.FLETC HER,J R. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents 

2. The insulated cable of claim 1 wherein said conductive material is carbon black.
 3. The insulated cable of claim 2 wherein the amount of said carbon black included in said blend is in the range of 27 - 75 percent. 